The invention relates to an electric steam iron comprising an electrically heated soleplate, said soleplate having at least one steam vent, a controllable steam generator for supplying steam to the at least one steam vent, and control means for controlling the steam generator.
An electric steam iron of the above type has been disclosed in European patent application No. 0 390 264.
In ironing of clothing three different processes can be distinguished: conditioning of the fibers, relaxation of the fibers and fixation of the fibers. During the conditioning the fibers are prepared for the relaxation. The conditioning is done by increasing the temperature of the fibers in order to make the fibers weak, which during the relaxation, enhance the recovery of the fibers from the plastic deformation caused by wearing of the clothing. The use of steam is an effective way to increase the temperature. Moreover, the weakness of some fibers also increases with the water content, especially for cotton, linen, viscose and wool. After the conditioning the relaxation or real ironing takes place. During the relaxation the weak fibers are being pressed between the soleplate and the ironing board. This should last sufficiently long to allow the fibers to recover from the plastic deformation. The moisture content of the fabric should not decrease too fast during relaxation in the case of cotton, linen and wool, as this would adversely affect the relaxation process. After relaxation the opposite from the conditioning takes place. This means that the weakness of the fibers is reduced to prevent the return of wrinkles. The fixation comprises the drying of the fibers, followed by cooling down.
During the conditioning the temperature of the fabric increases to about 100xc2x0 C., partly by condensation of steam and partly due to heating by the soleplate. During the relaxation the temperature should be kept at about 100xc2x0 C. to maintain both a high temperature and a high moisture content of the fabric, which provides for a fast recovery of the fibers. After the relaxation the fabric is being dried, indicated by a temperature increase in the fabric above 100xc2x0 C., and followed by cooling down to assure a proper fixation. This cooling down takes place partly on the ironing board and partly after removal of the cloth from the board to clear the board for the next cloth.
In conventional steam irons the steam rate is set and the iron is moved forwards and backwards over the fabric. In the forward stroke the amount of steam is insufficient in most cases to heat the fabric up to 100xc2x0 C., whereas after passing of the steam vents the fabric is heated further by the soleplate to a higher temperature closer to 100xc2x0 C. In the backward stroke the production of steam still continues, but the fabric will already reach 100xc2x0 C. and will not adsorb much water. Although it does not affect the fabric, steam is wasted that could have been used to warm up and more intensively moisten the fabric in order to obtain a weaker fabric at a higher temperature during the forward stroke. Unused steam is blown through the fabric into the ironing board and to the surrounding air without the desired condensation onto and in the fabric. Thus, a lot of heat and water is wasted.
In the steam iron disclosed in the above mentioned European patent application No. 0 390 264 waste of steam is reduced by controlling the amount of steam produced by the steam generator as a function of time. The steam generator includes a steam chamber which is designed as a pressure tank and in which a buffer stock of steam is formed, which is released at the beginning of an ironing cycle. The amount of steam produced starts with a high value and decreases more or less from that value linearly to a lower value. The steam production is controlled by regulating the output power of an additional heating element specifically provided for the steam buffer chamber. It is further known to adapt the steam production in said known steam iron to the amount of heat required to heat the fabric, by measuring the power need of the heating element of the soleplate. Such measuring, however, is inaccurate and slow.
An electric steam iron having an improved steam generation as compared to the iron disclosed in EP-A-0 390 264 is disclosed in U.S. Pat. No. 5,642,579. In accordance with U.S. Pat. No. 5,642,579 a steam iron comprises a fabric temperature sensor for detecting the temperature of the fabric to be ironed and control means responsive to a signal from the fabric temperature sensor for controlling the amount of steam produced. Thus steam generation is controlled by the fabric temperature and this is done in such a manner that steaming is stopped when a predetermined fabric temperature of about 100xc2x0 C. or a slightly lower temperature is reached. A cool fabric automatically triggers the steam production and the steam production is automatically shut off when the fabric has reached the predetermined fabric temperature.
In accordance with the present invention the steam production does not depend upon a buffer stock in a heated pressure tank. Moreover, the steam production is not based on the temperature of the fabric being ironed but on the soleplate temperature. More in particular, in accordance with the present invention each soleplate temperature value or range of values corresponds to a specific steam generation pattern comprising a substantially constant peak steam rate during a first time interval and a substantially constant lower peak steam rate during a second time interval.
The invention provides an improved electric steam iron comprising an electrically heated soleplate, said soleplate having at least one steam vent; a controllable steam generator for supplying steam to the at least one steam vent and control means for controlling the steam generator, wherein the steam iron further comprises temperature sensor means for sensing the temperature of the soleplate, said temperature sensor means in use supplying a temperature dependent signal to the control means, and wherein the control means is arranged to activate the steam generator in accordance with a predetermined steam pattern comprising at least a first phase of a first predetermined duration, in which steam is supplied at a substantially constant peak steam rate, and at least a second phase, in which steam is supplied at a substantially constant lower steam rate, wherein at least said peak steam rate depends upon the soleplate temperature.